1. Field of the Invention
The invention relates to an endless metallic belt formed by annularly arranging multiple plate-shaped elements that face each other, and passing an endless metallic ring through the elements so as to annularly join the elements. More particularly, the invention relates to a peripheral length adjusting apparatus and a peripheral length adjusting method which improves an accuracy of a peripheral length of an endless metallic ring.
2. Description of the Related Art
There is a vehicle including a continuously variable transmission (hereinafter, referred to as “CVT”) which continuously adjusts a speed ratio according to a running state of the vehicle. The CVT can efficiently transmit an engine output, and contributes to improving fuel efficiency and running performance. In one of CVTs that are put into practical use, a metallic belt and a pair of pulley are used, and an effective radius of each pulley is changed by a hydraulic pressure such that the speed ratio is continuously changed. In this CVT, an endless metallic belt is wounded on an input side pulley fitted to an input shaft and an output side pulley fitted to an output shaft. Each of the input side pulley and the output side pulley includes a pair of sheaves in which a groove width can be continuously changed. By changing the groove width of each of the input side pulley and the output side pulley, a belt-winding radius with respect to each of the input side pulley and the output side pulley is changed. Thus, a ratio between the rotational speed of the input shaft and the rotational speed of the output shaft, that is, the speed ratio can be continuously changed.
Conventionally, a metallic ring which is used for such an endless metallic belt is produced in the following manner. First, both ends of a thin plate of super-strong steel such as maraging steel are bonded by welding such that a ring-shaped drum is formed. Then, the drum is cut at a predetermined width, and is rolled out, whereby a metallic ring with a predetermined thickness is obtained. The metallic ring with the predetermined thickness obtained by rolling is subjected to solution heat treatment, and then peripheral length adjusting processing, whereby the peripheral length of the metallic ring is adjusted to a desired peripheral length. Further, the metallic ring is subjected to aging treatment and nitriding treatment, whereby hardness of the metallic ring is increased. Plural metallic rings with peripheral lengths which are slightly different from each other are laminated to be used for the endless metallic belt. Accordingly, the peripheral length adjusting processing is extremely important for laminating plural metallic rings to be used for the endless metallic belt.
Japanese Patent Laid-Open Publication No. 11-290971 discloses a peripheral length adjusting apparatus which performs peripheral length adjusting processing. The apparatus includes a drive roller and a driven roller on which a metallic ring is wound, and a correction roller which is provided between the drive roller and the driven roller.
In the peripheral length adjusting apparatus disclosed in Japanese Patent Laid-Open Publication No. 11-290971, the metallic ring is wound on the drive roller, the driven roller, and the correction roller. First, the driven roller is displaced such that the metallic ring is tensed. Then, while the drive roller is rotated, a displacement amount of the driven roller is measured by a displacement sensor with the metallic ring being tensed. An actual peripheral length of the metallic ring is calculated based on a center distance between the drive roller and the driven roller. Based on a difference between the actual peripheral length thus obtained and a desired peripheral length, a displacement amount of the correction roller, which is required for adjusting the peripheral length of the metallic ring to the desired peripheral length, is calculated. By applying urging force to the correction roller so as to move the correction roller by the calculated displacement amount, the metallic ring is plastically deformed. When the actual displacement amount of the correction roller matches the calculated displacement amount, application of the urging force to the correction roller is cancelled. The actual peripheral length of the metallic ring after the adjusting processing is calculated based on the center distance between the drive roller and the driven roller while the metallic ring is tensed by the driven roller. A difference between the actual peripheral length after the adjusting processing and the desired peripheral length is obtained. When the actual peripheral length matches the desired peripheral length, the operation is finished.
According to such a peripheral length adjusting method, an operation of applying the urging force to the correction roller needs to be repeated plural times until the actual peripheral length of the metallic ring is adjusted to the desired peripheral length, which is troublesome. Japanese Patent Laid-Open Publication No. 2001-105050 discloses a peripheral length correction method for a metallic ring which can adjust a peripheral length of a metallic ring to a desired peripheral length easily and reliably.
The peripheral length correction method disclosed in Japanese Patent Laid-Open Publication No. 2001-105050 includes the steps of winding a metallic ring on a drive roller and a driven roller which can be relatively displaced in a displacement direction so as to be away from each other, and a correction roller which is provided between the drive roller and the driven roller, and which can be displaced in a direction orthogonal to the displacement direction of the drive roller and the driven roller; maintaining the drive roller and the driven roller at a predetermined interval, and displacing the correction roller by a predetermined displacement amount with respect to a reference value of the peripheral length of the metallic ring in the direction which is orthogonal to the displacement direction of the drive roller and the driven roller and in which the metallic ring is stretched; obtaining an actual peripheral length of the metallic ring which is wounded on the drive roller, the driven roller, and the correction roller, while the drive roller and the driven roller are relatively displaced in the displacement direction so as to be away from each other by predetermined force, and the metallic ring is tensed by the drive roller and the driven roller; comparing the actual peripheral length of the metallic ring and the reference value of the peripheral length of the metallic ring so as to obtain a difference therebetween; and correcting the displacement amount of the correction roller according to the difference between the actual peripheral length of the metallic ring and the reference value.
According to the peripheral length correction method disclosed in Japanese Patent Laid-Open Publication No. 2001-105050, the drive roller and the driven roller on which the metallic ring is wounded are maintained at the predetermined interval, and the correction roller which is provided between the drive roller and the driven roller is displaced in the direction which is orthogonal to the displacement direction of the drive roller and the driven roller, and in which the metallic ring is stretched, whereby the metallic ring is plastically deformed, and the peripheral length is adjusted. Basically, the correction roller is displaced by the predetermined displacement amount with respect to the reference value of the peripheral length of the metallic ring. As the reference value, for example, a value which is set, for design and process management, as the peripheral length of the metallic ring after the rolling processing and the solution heat treatment is employed. The actual peripheral length of the metallic ring is obtained while the drive roller and the driven roller are relatively displaced in the displacement direction so as to be away from each other by predetermined force, and the metallic ring is tensed by the drive roller and the driven roller. Then, the difference between the actual peripheral length and the reference value is obtained, and the displacement amount of the correction roller is adjusted according to the difference. Therefore, the displacement amount of the correction roller with respect to the actual peripheral length can be obtained based on the reference value. Accordingly, the peripheral length of the metallic ring can be adjusted to the desired peripheral length easily and reliably by performing the operation of displacing the correction roller only once, and the yield can be enhanced.
After the endless metallic ring whose peripheral length is thus adjusted is removed from the drive roller and the driven roller, the peripheral length of the endless metallic ring is contracted due to elastic deformation, as compared with when the peripheral length is adjusted. It is possible to enlarge the interval between the rollers for adjusting the peripheral length considering such a contraction amount of the peripheral length (hereinafter, referred to as “spring back amount”). However, the spring back amount varies according to the peripheral length of the endless metallic ring before adjustment. Since the peripheral length of the endless metallic ring before adjustment has a deviation, the accuracy of the peripheral length of the endless metallic ring deteriorates.